It is well known that grease manufacturing can be either continuous or non-continuous. Both processes react solid or aqueous base e.g. lithium hydroxide monohydrate with carboxylic acids in the presence of mineral oil. The reaction of lithium hydroxide monohydrate and the carboxylic acid acts to thicken the mineral oil to produce straight lithium greases. The most commonly used carboxylic acid used in the manufacture of grease is 12-hydroxystearic acid.
Non-continuous and continuous processes to prepare said greases require high temperatures for saponification and high pressure vessels.
U.S. Pat. No. 2,434,539 relates to a continuous method of preparing anhydrous grease by initially dehydrating metal hydroxide before addition into a slurry with high molecular weight fatty acid.
U.S. Pat. No. 2,444,720 relates to the manufacture of lubricants containing lithium grease by intimately reacting anhydrous lithium hydroxide or lithium hydroxide monohydrate with fatty acids at a temperature in the range 35 to 45° C. for sufficient time for 90 weight percent of lithium and fatty acid compounds to form a grease.
U.S. Pat. No. 2,659,695 relates to the preparation of a grease from an insoluble metal hydroxide and a fatty acid with a water in oil emulsion containing petroleum mahogany sulfonates dissolved in mineral oil.
U.S. Pat. Nos. 2,708,659 and 2,868,729 relate to methods of preparing grease by initially dissolving calcium hydroxide in lubricating oil before the addition of the appropriate organic acid. The organic acid used in U.S. Pat. No. 2,868,729 is a substituted alkenyl succinic acid, whereas U.S. Pat. No. 2,708,659 uses acids such as stearic, oleic, tallow etc.
U.S. Pat. No. 4,075,234 relates to grease manufacture using a concentrated aqueous solution of lithium hydroxide in a liquid reaction mixture comprising an alkyl nitrile.
U.S. Pat. No. 4,337,209 relates to a method of preparing soap and greases by reacting an organic carboxylic acid, its esters and mixtures thereof with a concentrated aqueous solution of alkali metal hydroxide in the presence of an inorganic salt, in a liquid reaction medium comprising acetone. The presence of the inorganic salt increases the yield of the soap or grease.
U.S. Pat. No. 5,236,607 relates to a process for preparing a lithium soap thickened grease which consists of heating a mixture of oil and a lithium base to at least 100° C., then heating the resulting mixture at a temperature in the range of 110° C. to 200° C. until a thickened grease is obtained.
U.S. Pat. No. 5,948,736 relates to a method of forming a dust free lithium hydroxide monohydrate by coating said hydroxide with 0.1 to 5 weight percent of low melting point or liquid fatty acids or esters. Triglycerides of fatty acids may also be used to coat lithium hydroxide monohydrate. Typically, the liquid fatty acids or esters of the invention have a melting point less than 38° C.
U.S. Pat. No. 6,153,563 relates to a method of decreasing environmental hazards associated with lithium hydroxide monohydrate or anhydrous lithium hydroxide in grease manufacture. The technology makes use of a sealed pouch of a single layer polyolefin film having a thickness of 0.0005 to 0.001 inches capable of melting below 138° C. The polyolefin is soluble in a lubricating oil base. The sealed pouch contains said hydroxide or lithium fatty acid or mixtures thereof for use in preparation of grease.
The “NLGI Lubricating Grease Guide, 2nd Edition, 1989” discloses water free (anhydrous) calcium greases prepared by reacting 12-hydroxystearic acid with lime in the presence of oil in the absence of a surfactant.
It would be desirable to have a grease composition and a manufacturing process having minimal environmental hazardous e.g. low dust or vapour and producing less foam. Furthermore it would be desirable if the process produced a higher yield value using less energy and raw materials.